The present invention relates to a method employed in a press section of a paper machine, particularly in a closed press section, for changing a pick-up fabric and/or press fabric, the substantial run of which when the fabric is in its normal operating position, passes above a group of nip defining press rollers of the paper machine. In the method, insert members provided in one of the side frame components of the paper machine frame are removed and the press nip or nips through which the fabric passes is opened for the changing of the fabric.
The invention further relates to apparatus for performing the method and a press section with which the method can be employed, preferably a so-called closed press section.
The use of pick-up and press fabrics made of synthetic plastic material has recently become increasingly common in paper machine press sections. Such fabrics are being used to replace the textile fabrics which have been conventionally employed in the past. However, the introduction of such new fabrics has resulted in problems arising in connection with the changing thereof when such change becomes necessary.
Thus, in the changing of conventional textile felts according to known techniques, the new or changing textile felt has, for example, been compressed in the sideways or cross-machine direction, and then spread out starting at one margin thereof and carried into the machine frame through gaps or spaces defined by insert members removed from the paper machine frame. The textile felt encircles those rollers which will be situated within and lapped by the felt loop during actual operation.
As noted above, however, the changing of fabrics formed of synthetic material, such as plastic, is quite difficult, expecially in the case of so-called closed press sections such, for example, as in a "Sym-Press II" (a trademark of Valmet Oy of Helsinki, FInland) press section. In order to more clearly illustrate these problems, the structural arrangement of a "Sym-Press" press section will now be described.
A "Sym-Press II" press section comprises at least one pick-up fabric and two press fabrics, namely a first fabric operating as the pick-up fabric and which additionally serves as a press fabric in the first and second press nips of the press section, and a second fabric operating as a second press fabric in the first nip.
Thus, the "Sym-Press" press section comprises a suction roller over which the first fabric passes. Two press nips are defined in conjunction with the suction roller, the first press nip constituting a two-fabric press nip defined by the suction roller and a recessed-surface press roller. The second press nip constitutes a single-fabric nip, defined by the suction roller and a smooth-surface roller such as, for example, a stone roller. A third press nip is defined by another press roller, such as a recessed surface roller, and the stone roller. A third fabric loop passes through the third press nip.